The Third Sodium Binding Site of Na,K-ATPase Is Functionally Linked to Acidic pH-Activated Inward Current
| Autor: | Jean-Daniel Horisberger, Käthi Geering, Ciming Li |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2018 |
| Předmět: |
Cation binding
Amino Acid Substitution Animals Binding Sites Female Hydrogen-Ion Concentration Membrane Potentials Models Biological Mutagenesis Site-Directed Na(+)-K(+)-Exchanging ATPase/chemistry/genetics/*metabolism Oocytes/metabolism Ouabain/pharmacology Potassium/metabolism Protein Structure Tertiary Rats Recombinant Proteins/chemistry/genetics/metabolism Sodium/metabolism Xenopus Physiology Xenopus Sodium Biophysics chemistry.chemical_element In Vitro Techniques Models Biological Membrane Potentials Extracellular Animals Binding site Na+/K+-ATPase Ouabain Binding Sites Cell Biology Hydrogen-Ion Concentration Recombinant Proteins Protein Structure Tertiary Rats Calcium ATPase Amino Acid Substitution chemistry Biochemistry Mutagenesis Site-Directed Oocytes Potassium Plasma membrane Ca2+ ATPase Female Sodium-Potassium-Exchanging ATPase Intracellular |
| Zdroj: | Journal of Membrane Biology, vol. 213, no. 1, pp. 1-9 |
| Popis: | Sodium- and potassium-activated adenosine triphosphatases (Na,K-ATPase) is the ubiquitous active transport system that maintains the Na(+) and K(+) gradients across the plasma membrane by exchanging three intracellular Na(+) ions against two extracellular K(+) ions. In addition to the two cation binding sites homologous to the calcium site of sarcoplasmic and endoplasmic reticulum calcium ATPase and which are alternatively occupied by Na(+) and K(+) ions, a third Na(+)-specific site is located close to transmembrane domains 5, 6 and 9, and mutations close to this site induce marked alterations of the voltage-dependent release of Na(+) to the extracellular side. In the absence of extracellular Na(+) and K(+), Na,K-ATPase carries an acidic pH-activated, ouabain-sensitive "leak" current. We investigated the relationship between the third Na(+) binding site and the pH-activated current. The decrease (in E961A, T814A and Y778F mutants) or the increase (in G813A mutant) of the voltage-dependent extracellular Na(+) affinity was paralleled by a decrease or an increase in the pH-activated current, respectively. Moreover, replacing E961 with oxygen-containing side chain residues such as glutamine or aspartate had little effect on the voltage-dependent affinity for extracellular Na(+) and produced only small effects on the pH-activated current. Our results suggest that extracellular protons and Na(+) ions share a high field access channel between the extracellular solution and the third Na(+) binding site. |
| Databáze: | OpenAIRE |
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